1. Field of the Invention
The present invention relates to an image processing method, etc., or in particular, to an image processing method, etc. for X-ray computer tomography.
2. Description of the Background Art
Conventionally, the panorama X-ray imaging apparatus for tomography along the dental arch is known in the field of dental diagnosis. In this panorama X-ray imaging apparatus, an X-ray source and an X-ray imaging means arranged in opposed relation to the X-ray source are moved along a predetermined trajectory with the head of an object located therebetween, thereby producing a panorama tomogram along the dental arch.
Also, in the field of dental diagnosis, the X-ray CT (computer tomography method) for tomographically imaging an arbitrary part of the human body is used. In this X-ray computer tomography apparatus, the X-ray source and the X-ray imaging means arranged in opposed relation to the X-ray source are rotated in a predetermined direction with the head of an object held therebetween, and the resulting image signal is processed by the computer. In this way, the X-ray projection data is reconstructed, so that a sectional image of an arbitrary part of the head, etc. cut at an arbitrary angle or a three-dimensional volume data can be obtained.
A method of producing a panorama tomogram from the X-ray projection data on the dentomaxillofacial region obtained from the X-ray computer tomography apparatus is disclosed in Japanese Patent Application Laid-Open No. 08-215192, Japanese Patent Application Laid-Open No. 2001-061834 and Japanese Patent Application Laid-Open No. 2000-057789. Specifically, Japanese Patent Application Laid-Open No. 08-215192 discloses a technique in which a plurality of coordinate points are input from the sliced images of the occlusal surface obtained by the X-ray computer tomography apparatus thereby to designate the panorama curve of the dental arch, so that the panorama image of the dental arch is displayed on the one hand and an oblique image (an arbitrary sectional view or an inclined sectional view) of the region of interest is displayed by designating the oblique line on the other hand.
Also, Japanese Patent Application Laid-Open No. 2001-061834 discloses a technique in which a reference curved surface and a curved thick plate region are designated from the three-dimensional volume data constituting the X-ray projection data subjected to CT reconstruction thereby to produce a panorama tomogram of the dental arch. Further, Japanese Patent Application Laid-Open No. 2000-057789 discloses a technique in which the three-dimensional distribution information on the projection line in the direction crossing the panorama layer plane at a predetermined angle is calculated based on the projection data obtained by the X-ray computer tomography, and the calculation result is developed on the two-dimensional plane thereby to generate a panorama tomogram.
In Japanese Patent Application Laid-Open No. 08-215192, Japanese Patent Application Laid-Open No. 2001-061834 and Japanese Patent Application Laid-Open No. 2000-057789, there is a common merit to obtain a panorama tomogram based on the X-ray projection data imaged by the X-ray computer tomography apparatus. That is the merit that by once obtaining the X-ray projection data imaged by the X-ray computer tomography apparatus required no image taking for obtaining a panorama tomogram. The merit also has further advantage of not being exposed to unnecessary X-ray. However, in Japanese Patent Application Laid-Open No. 08-215192, a problem involved in immense amount of time and effort has arisen that at the time when displaying the panorama tomogram and the oblique image from the imaged data, a complicated operation such as inputting a plurality of coordinate points and parameters is required. Similarly, in Japanese Patent Application Laid-Open No. 2001-061834 and Japanese Patent Application Laid-Open No. 2000-057789, there has been a problem that in order to obtain the panorama tomogram, it is necessary for an operator to conduct a complicated operation such as setting a reference curve. Otherwise he/she is not allowed to obtain the panorama tomogram with ease.